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<h1><a href="https://archiveofourown.org/works/25145230">Eternally</a> by <a class='authorlink' href='https://archiveofourown.org/users/hyukasplushie/pseuds/hyukasplushie'>hyukasplushie</a></h1>

<table class="full">

<tr><td><b>Series:</b></td><td>sookai/soobning abo aus [1]</td></tr>

<tr><td><b>Category:</b></td><td>TOMORROW X TOGETHER | TXT (Korea Band)</td></tr>

<tr><td><b>Genre:</b></td><td>Alpha Choi Soobin, Alpha/Beta/Omega Dynamics, Bottom Huening Kai, Knotting, M/M, Marking, Mating Cycles/In Heat, Omega Huening Kai, Omega Verse, Possesive Choi Soobin, Shameless Smut, Top Choi Soobin</td></tr>

<tr><td><b>Language:</b></td><td>English</td></tr>

<tr><td><b>Status:</b></td><td>Completed</td></tr>

<tr><td><b>Published:</b></td><td>2020-07-08</td></tr>

<tr><td><b>Updated:</b></td><td>2020-07-08</td></tr>

<tr><td><b>Packaged:</b></td><td>2021-05-05 02:42:25</td></tr>

<tr><td><b>Rating:</b></td><td>Explicit</td></tr>

<tr><td><b>Warnings:</b></td><td>Creator Chose Not To Use Archive Warnings</td></tr>

<tr><td><b>Chapters:</b></td><td>1</td></tr>

<tr><td><b>Words:</b></td><td>3,502</td></tr>

<tr><td><b>Publisher:</b></td><td>archiveofourown.org</td></tr>

<tr><td><b>Story URL:</b></td><td>https://archiveofourown.org/works/25145230</td></tr>

<tr><td><b>Author URL:</b></td><td>https://archiveofourown.org/users/hyukasplushie/pseuds/hyukasplushie</td></tr>

<tr><td><b>Summary:</b></td><td><div class="userstuff">
              <p>Soobin was an alpha, and he was an omega. This wasn't good. Yes, he was attracted to his big brother’s bestfriend, always had been since the start, but as he'd thought himself to be a beta, he'd resigned himself to the fact that alphas didn't mate with beta's, so he didn't have a chance.</p><p>It was different now. Because Kai was an omega.</p>
            </div></td></tr>

<tr><td><b>Relationships:</b></td><td>Choi Soobin &amp; Huening Kai, Choi Soobin/Huening Kai</td></tr>

<tr><td><b>Series:</b></td><td>sookai/soobning abo aus [1]</td></tr>

<tr><td><b>Series URL:</b></td><td>https://archiveofourown.org/series/1846360</td></tr>

<tr><td><b>Comments:</b></td><td>4</td></tr>

<tr><td><b>Kudos:</b></td><td>164</td></tr>

</table>

<a name="section0001"><h2>Eternally</h2></a>
<div class="story"><div class="fff_chapter_notes fff_head_notes"><b>Author's Note:</b><blockquote class="userstuff">
      <p>Thank you so much for reading! Hope you guys enjoyed &gt;3&lt;</p>
    </blockquote></div><div class="userstuff module">
    
    <p>The first thing Kai noticed that was out of the ordinary was the sudden heat. He pulled at his collar and tie, fanned his rosy face with his hand, before removing his sweater vest altogether. His breath quickened as he looked around at his classmate, all of whom looked quite comfortable with the room temperature, not even a flush on any of their faces. He frowned in confusion, loosening his tie further as the heat radiated down his neck and chest. He could feel his white shirt dampening with sweat, slowly sticking to his burning flesh.</p><p>Then the tingling began. It started in the bottom of his stomach, before spreading throughout his entire body, the feeling making his fingers twitch and his mind swim. Amongst the tingling an almost pleasant ache settled in his pelvis and thighs.</p><p>The young man took a deep breath, and slumped forward, resting his face in his hands. He bit his lip hard, in an attempt to hold in the moan that threatened to escape his mouth as his hips shifted position, the pressure being relieved from one spot and relocated to another.</p><p>What was happening to him?</p><p>Kai sat still for the next few minutes, struggling to sort his thoughts out through the haze that had descended on his mind, and stop himself from making embarrassing noises every time he moved in his chair.</p><p>He thought that he could probably deal with whatever was happening to him for a bit longer, as there was only an hour until clocking off time. That was until he felt a definite warm dampness slowly spreading against the seat of his boxers.</p><p>"Oh god…No, no, no…This can't be happening." He muttered under his breath, his heart thumping against the inside of his ribcage, the panic settling in his stomach.</p><p>Kai wasn't in heat. He <em>couldn't </em>be in heat. He was a beta, he'd always been a beta and was quite happy being one. He didn't have any of the alpha aggressiveness or dominance, but nor was he viewed by society as an omega; an inferior, walking baby incubator.</p><p>It had been known in the past for previously classified betas to suddenly come into heat and be revealed as a slow developing omega. But the poor individual often had trouble adjusting. They had to change profession most of the time (as omegas were not permitted to work in some jobs), they also had to deal with the label and stigma that society placed on omegas being there for two reason, for an alphas enjoyment and to produce young pups. They also often had to accept that as an omega it is likely that they would never have a child with someone that they loved, as when in heat, as bad as it sounds, instincts take over and any suitable alpha will do.</p><p>Kai had never been disappointed being classified as a beta, it was the easiest of the three to be and you could choose who you had relationships with, rather than being a slave to pheromones and instincts.</p><p>The average heat lasted for five days and occurred once every three months or so. Most un-bred omegas without alphas had to shut themselves away for the duration of their heat, unable to function within society, both physically and mentally. It could also be dangerous for an unattached omega to be around a number of alphas, as even the most gentlemanly alpha could become violent and unable to fight off once they got the scent of an omega in heat.</p><p>Because he was obviously not a beta, he had to get out of this office and away from everyone. Now!</p><p>He looked around at the others (all beta's), who for the most part still seemed oblivious to his current crisis. Beta's could just about sense when an omega was in heat, but they weren't affected by it the way alphas were, which was a blessing in disguise. Taehyun however was looking at him with a small crease between his eyebrows, and the occasional flaring of his nostrils telling Kai that he could smell him.</p><p>Shit.</p><p>Somehow he had to get home without attracting unwanted attention from any alphas in the building or on the street.</p><p>He was fucked. Both literally and metaphorically.</p><p>Kai was only getting more flustered the longer he sat there, all of the sensations getting worse, he was hot, there was a sheen of sweat across his flesh as well as his usually pale skin being flushed bright red. Not to mention the increasing dampness on the seat of his underwear.</p><p>"Oh god…" as he shifted he couldn't stop the frustrated moan that escaped his lips, luckily he was able to muffle most of it, but not without getting another look from Taehyun, who now had an expression of slight sympathy.</p><p>He knew what was happening to him and it wouldn’t be long before the others noticed it too.</p><p> </p>
<hr/><p>Soobin had been studying day in the library, doing the assignment from his biology class. It was taking forever. Especially since all afternoon Soobin had been distracted every few minutes by that damn smell. He knew what it was. There was obviously an omega close by who was in heat, either in the station or close to it. Why wasn't the omega at home? They always shut themselves away during a heat. And as an alpha, Soobin was grateful that they did, it was hard enough controlling himself when he got a whiff of an omega's heat far away when walking on the street. But to be in the same building or in close proximity to one? It made it so much harder to stop himself.</p><p>It might be a witness, but even then, an omega wouldn't put themselves at risk going out when their heat was due. It was driving Soobin insane. He'd been half hard for the past hour and a half, and had used his balm four times already to rid himself of the ache behind his eyes, caused by the overpowering scent.</p><p>The omega had obviously only just begun their heat, he could tell by the strength of the smell, it started off being bearable, but now it was almost suffocating. The omega must be in the building, it wouldn't be this strong otherwise.</p><p>Soobin would go and get a drink of water and try to cool himself down.</p><p>The second he stepped out of the library into the lounge it was like being slapped in the face. The smell was overpowering, the omega must be very close. How could anyone be sitting happily chatting? God, it was so hot in here. Soobin tugged at his shirt collar and hurriedly made his way through the cluttered room, wanting nothing more than to give into those base desires, but he wasn't about to go and breed some random omega because he couldn't control himself.</p><p>That thought kept him walking until he came over a bench where he stopped so suddenly in his tracks that he almost made himself overbalance. With a mixture of arousal and shock he turned on the spot to face someone familiar, the omega scent still rolling towards him in waves, making his mouth water and his breath hitch.</p><p>“Huening Kai.”</p><p>The one he called Kai looked as mortified as Soobin felt. His cheeks were so flushed he looked like he'd just ran a marathon, while his breathing gave a similar suggestion. There was a thin sheen of sweat on his forehead and he seemed to be sitting gingerly in his seat, trying not to move too much.</p><p>Kai was the <em>omega</em>? How can he be? He was his bestfriend little brother and last time he checked Kai presented as a beta. He should have known, shouldn’t he? Yeonjun would have told him. Besides, Soobin had never smelt a whiff of a heat on Kai before either. He was sure he was a normal regular beta, like most other individuals.</p><p>Obviously not. Either way, the scent was too much for Soobin to take. He took another step forwards towards the young man, attracting his attention. Kai looked up at him for a second, and they both realized what the other knew.</p><p>For a moment Kai's eyes widened like a deer caught in headlights, before he stood up and practically ran out of the lounge, leaving behind a very aroused, slightly confused Soobin.</p>
<hr/><p>Kai splashed cold water over his burning face, the shaking in his entire body not helping.</p><p>Soobin was an alpha, and he was an omega. This wasn't good. Yes, he was attracted to his big brother’s bestfriend, always had been since the start, but as he'd thought himself to be a beta, he'd resigned himself to the fact that alphas didn't mate with beta's, so he didn't have a chance.</p><p>It was different now. Because Kai was an omega.</p><p>But did he really want to have Soobin just because their bodily chemicals told them they should? He was much more enamored with the beta ideal of being with someone because you loved them. Soobin didn't love him, he was just drawn to him by his heat scent, like any other wild animal.</p><p>Kai had to get home.</p><p>The young man's head shot up to look in the mirror as the door to the toilets opened, revealing the alpha he had just avoided.</p><p>Kai took a deep breath as Soobin came closer and tried to ignore the pulse that thrummed through his veins and body at an alpha being so close to him.</p><p>When the alpha spoke, his voice was husky and rough.</p><p>"You're an omega." It wasn't a question.</p><p>Kai let out a moan at the alphas voice. "I d-didn't know. I thought I was a beta. I've n-never had a heat before." the omega choked out, the urge to just turn to Soobin a beg was so strong, but he resisted, he was still in control of his actions, even if he was in heat.</p><p>Soobin had his eyes closed and seemed to be trying to breath evenly, his hands clenched into fists. It was a few seconds before he spoke.</p><p>"You need to get home. You can't go by yourself, you'll be vulnerable." He paused for a second, as if considering what he was going to say next was a good idea. "I'll drive you."</p><p>Kai let out another moan. "N-No, it’s okay. It'll be easier if a beta drives me home. They won't be affected in the same way."</p><p>"No! I'll do it." Soobin's voice was suddenly very clear and forceful, as was his expression. That would be the alpha aggression and possessiveness. Even Soobin wasn't above it.</p><p>The young omega bit his lip and nodded. "Ok."</p>
<hr/><p>The ride to Kai’s flat was charged to say the least. Kai was curled up in the passenger seat, as far away from the other man as possible, trying to make it easier for him, so he didn’t have to smell him to such an extent. While Soobin, gripped the steering wheel with both hands so hard his knuckles were white, and his eyes didn’t deviate from the road. He looked like he was barely able to control himself, and Kai could see the evidence easily when he glanced down to the alpha’s lap. He felt sorry for him really.</p><p>Kai knew that he should have gotten a beta to drive him home.</p><p> </p>
<hr/><p>Once they were there, both men quickly climbed out of the car and made their way up to the flat, Soobin walking close behind Kai, licking his lips at the strong scent in the young man's wake.</p><p>As Kai was busy fiddling with the keys to the door another man, older than Kai, but younger than Soobin, walked down the corridor towards the stairs. He was an alpha, and immediately caught Kai's scent, staring at him wantonly. The omega fumbled with the keys even more at this attention.</p><p>Soobin wasn't having any of that. He moved closer to the dark haired omega, before placing a hand on the small of his back and glared viciously at the other man, who quickly realized the situation, ducked his head and moved on quickly.</p><p>Kai was <em>his,</em> no other alpha could even look at him.</p><p>Wait, what? Kai wasn't his. He was just taking him home. But, oh god he wished he was his. He <em>should </em>be his.</p><p>He <em>would </em>be his.</p>
<hr/><p>Finally Kai managed to get the door open, before hurrying inside his flat safely and flinging his keys on the table. He was so relieved to be home away from prying eyes and interested stares, that he gave a small cry of surprise when he felt Soobin grab him from behind and slam him back against the font door, before gripping both of his wrists in his stronger hands and pinning them against the door above his head.</p><p>The skin to skin contact was like a fire erupting along his flesh, burning him, but feeling good at the same time. Looking up into Soobin's eyes, he could see that they were clouded with want and lust, entirely chemical, no real emotions behind them, but still it was enough to make Kai groan, when paired with the hard arousal he could feel pressed against his stomach.</p><p>When their lips met in a passionate kiss, Kai was sure his entire body gave off an extra wave of pheromones, making sure that Soobin wouldn't be able to stop. It was completely involuntary, his reaction, he kissed back with fervor almost forgetting that previously in the bathroom he'd not wanted to give in to this and be with Soobin. It wasn't right.</p><p>As Soobin broke the kiss and began to trailer them along Kai's jaw line and neck the Omega spoke up, his voice shaky and clouded heavily with arousal.</p><p>"H-Hyung, no. Please. You-you don't want this." he muttered, pushing the other man away, but putting no real effort into it.</p><p>Soobin pulled away to look at Kai for a second.</p><p>"Yes I do. I could smell you all afternoon."</p><p>Kai shook his head, every ounce of fight in him quickly disappearing.</p><p>"N-No, it's the alpha in you that wants this. We d-don't have to."</p><p>Soobin lips brushed Kai's ear, sending shivers up his spine.</p><p>"Maybe, but I still want you, ever since Yeonjun introduced the two of us three years ago. And the omega in you also wants me, your body is telling you that." He whispered into the smaller mans ear. "Listen to it, Kai."</p><p>With that the omega wrapped both arms around Soobin's neck and reunited their lips harshly. It was a messy kiss, their teeth clashed painfully two times, but neither cared.</p><p>It wasn't long before Kai was backing himself up to wards the bedroom, pulling the alpha with him and thanking every deity known to man that his brother was out with his friends. They were both stripped of their clothing very quickly, the need to feel skin to skin more important than the casualties of buttons that were ripped off in their haste.</p><p>When both men were completely naked, Soobin could finally smell Kai uninhibitedly, the scent of heat, arousal and readiness to mate was rolling off of him in waves, that crashed mercilessly against Soobin, overwhelming his senses and short-circuiting his normally rational thoughts.</p><p>Soobin insistently pushed Kai back onto the bed, before crawling on all fours towards the prone omega. Kai was laid out on his back, his knees bent and slightly apart, waiting for Soobin to settle between them.</p><p>The alpha lend down and kissed the young omega, while pushing his knees further apart with one hand. He stroked his fingers down one side of Kai's face in an unusually comforting gesture, before the hand travelled lower and lower, then slipping under.</p><p>He could feel that the backs of Kai's thighs were wet, the effects of the heat making him ready for mating. He followed the wet trail of clear fluid until he came to the young man's entrance. His finger slipped in easily, the omega's body not resisting, but accepting the intrusion, craving it in fact.</p><p>Kai let out a loud wanton moan at the sensation of just one finger inside of him. It was amazing, but It wasn't enough. He pushed his body down onto Soobin's finger encouraging more.</p><p>The young man's own lubricating fluids eased Soobin's actions, allowing him to quickly slip in a second and third finger. He didn't really need to stretch Kai at all, his body was ready, he was in heat, he wanted it. But the small, rational, non-alpha part of Soobin's brain that still functioned properly told him that he would hate to hurt Kai. That told him to make sure the younger man was ready, so ignoring his instincts that told him to just take, he prepared the flushed omega below him, watching for any signs of discomfort.</p><p>When he was sure Kai was ready, he removed his fingers, growling slightly at the needy cry Kai gave at his movement. He then gripped the back of one milky white thigh and lifted it to his shoulder, while Kai wrapped the other leg around Soobin's waist.</p><p>"P-Please…"</p><p>With one smooth movement Soobin pushed inside, both men gasping breathlessly at the feeling. All Soobin wanted to do was pound away, no thought for the omega beneath him, but this wasn't just any omega, this was Kai, his bestfriend little brother, a whole angel. Soobin wouldn't hurt him, so he waited, giving the young man a minute to adjust.</p><p>Kai was overwhelmed with sensations, all of his senses interlacing, his brain not clear which feeling was coming from which stimulus. All that he could say that being an omega may be second class in society, but at that moment he didn't care. The feeling of being in heat and wanting an alpha so badly, then finally being filled after all of that anticipation. It was the most intense feeling Kai had ever experienced, and Soobin hadn't even moved yet.</p><p>The dark haired man gripped Soobin's biceps hard enough to bruise, before digging the heel of his foot into the other man's lower back, forcing him to move.</p><p>It took a couple of thrusts for Soobin to find that one little spot, but when he found it he didn't stop hitting it, every sound that came out of Kai's mouth urged the alpha on, each thrust becoming harder and more satisfying.</p><p>Kai dragged Soobin down for a wet, sloppy kiss, the knee of the leg resting on Soobin's shoulder almost touching his own. The two men moaned into each others mouth, uncaring of the heat, the sweat and the fluids that surrounded and covered them both.</p><p>They were both close, the trembling of Kai's thighs told Soobin that. The alpha braced himself with one hand placed on the mattress next to Kai's head, while the other gripped his erection and stoked in time with the snap of his hips. It wasn't long before the young omegas cries climbed in volume and his back arched as he came against the alpha's chest and his own stomach.</p><p>The noises from his omega beneath him and the contractions around him finally pulled Soobin over the edge, his completion ending in a low, possessive grunt.</p><p>In less than a few seconds both men felt the beginnings of the knot connecting them together form anywhere between a few minutes to a complete hour. When It was fully developed Kai let out a little moan at the completely full feeling, while Soobin's breath hitched at the increasing tightness around him.</p><p>As both of their breathing and their hearts slowed down Kai lifted his head and gently kissed the alpha, who responded in kind. Their needs sated for now, Kai's omega scent changed slightly, from one of him in the throws of his first heat, to something a little more content, but just as addictive to Soobin's alpha nature.</p><p>It took a minute or two of awkward and careful movements but eventually Soobin was spooned up behind Kai, the two still connected, waiting for the knot to go down.</p><p>Soobin gently nuzzled Kai's neck and hairline inhaling the ever present omega scent, his member twitching inside of the young man with every movement and contraction of the body in front of him.</p><p>"Mmm…<em>my </em>Omega…" He sank his teeth into Kai's neck, enough to leave a mark, encouraged by the sharp gasp it brought. "<em>Mine</em>…"</p><p>Kai didn't know if it was the hormones and pheromones making Soobin say those things, but at the moment, he really didn't care. They were both doing what alphas and omegas were meant to do, what they were made to do. He also knew that what they were doing was risky, omega fertility was much higher than that of betas, especially during a heat.</p><p>But with Soobin finally breathing possessive, sweet words into his ear, Kai really couldn't care less.</p>
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